The concept of mechanically manipulating the ideal gas laws to convert heat into motion or vice-versa was first patented by Robert Stirling in 1817. Since that time several designs, most utilizing multiple pistons, have emerged including some designs utilizing pressure waves in lieu of a displacer with only a single piston.
The basic Stirling engine includes a trapped gas that is heated or cooled which then expands or contracts (according to the ideal gas laws) which pushes or pulls on a piston which then drives a crankshaft. The crankshaft is typically coupled to a flywheel and an output shaft. The output shaft delivers usable mechanical force relative to the initial temperature differential and amount of heat transferred.
Current commercial designs utilize a piston style displacer to move the working gas from a heating chamber to a cooling chamber and back. Common designs use multiple internal seals and two or more pistons. Current designs are complex and difficult to manufacture making them relatively high cost. The greater efficiency, reliability, lifespan, cleanliness, and flexibility that Stirling engines demonstrate compared to internal combustion engines has previously been sacrificed in favor of the faster start up, control response, greater power density, and ease of manufacture of competing engines. However, the inherent advantages of the Stirling engine allows it to compete successfully in various specialty niches of the engine market, such as satellite power production, waste heat recovery, cryogenics, solar power conversion, space craft, and submarines, where faster start up, control response, greater power density, and ease of manufacture are not the critical criteria in engine selection.
The Stirling engine has many advantages such that it could displace internal combustion engines in many applications if a few of the Stirling engine's drawbacks could be addressed. For example the Stirling engine has fewer moving parts, no need for expensive sound deadening or exhaust gas treatment, nor complex ignition, timing, and fuel handling requirements. Furthermore, the Stirling engine benefits from a large menu of energy sources and fuels to choose from and the use of non-polluting gasses when used in refrigeration.
Accordingly, there is a need for a Stirling engine with lower cost, and higher power density. Such an improved Stirling engine could become the mainstream choice in such applications as hybrid automobiles, aircraft, and boats, as well as electric generators, refrigerators and water heaters. In other words, applications in which costs, simplicity and power density are the primary consideration and where start up speed and control response are ancillary considerations.